Comprised of building blocks known as amino acids, proteins contain car bon, hydrogen, oxygen, nitrogen, and sometimes sulfur. One of the most important functions of proteins is their role as enzymes or catalysts. Enzymes accelerate chemical reactions in the body without additional energy, such as heat.

There are specific enzymes for specific reactions. The digestive system provides some excellent examples. The enzymes that react to digest starches are different from those that digest lipids in food.

Because there are many thousands of different chemical reactions going on in the body at one time, there are many thousands of different enzymes.